Gradual deamidation of amino acids, such as asparagine, in proteins over time can cause a reduction in protein stability. When proteins, particularly antibodies, are used as pharmaceutical agents for various diseases, they are required to be stable over a long period. However, the activity of antibodies decreases with time. The cause for reduction in activity varies in antibodies. Deamidation of amino acids such as asparagine in the antibody is known to be one of the causes.
Therefore, proteins can be stabilized by suppressing deamidation of asparagines. Thus, research on suppressing deamidation of asparagine has been conducted. Substitution of asparagine with another amino acid by site-directed mutagenesis is considered the most certain method to prevent deamidation of proteins. However, such a substitution has the potential to influence protein activity. For example, when the asparagine is located in the complementarity determining region (CDR) of an antibody, such substitution is reported to affect the antibody binding affinity (Presta L. et al., Thromb. Haemost. 85: 379-389, 2001). An anti-human tissue factor (TF) antibody that is expected to inhibit thrombus formation without inhibiting the extrinsic blood coagulation reaction via the inhibition of Factor X activation mediated by TF in the intrinsic blood coagulation reaction is known in the art (WO 99/51743). This antibody has not been formulated as a pharmaceutical preparation, and its activity reduces over time under antibody destabilizing conditions. The deamidation of the anti-human TF antibody is supposed to be a factor in such reduction.
Thus, a method to suppress deamidation of asparagine without influencing antibody activity has been desired in the art.